A “security system” has been proposed in which intruders are detected by using a laser range finder that uses laser light as its light source (e.g., see Patent Document 1). Also, an “object distinction method using an area sensor” has been proposed in which laser light is used to accurately distinguish pedestrians or the like, although it is slightly different from security devices or security systems (e.g., see Patent Document 2).
Furthermore, in view of problems in these conventional techniques, the inventor of the present invention has already proposed a laser area sensor in which it is possible to easily set an appropriate security region with which detection errors can be prevented as much as possible according to the actual installation site or security purpose, and in addition, it is possible to easily set an arbitrary security region (see Patent Document 3).
On the other hand, in apparatuses that detect intruders by using a laser range finder or apparatuses that are mounted on a vehicle and measure the distance to the vehicle in front thereof, dirt on the cover of the laser light receiving portion or the like may have an adverse influence on measurement accuracy. Therefore, various techniques for detecting such dirt have been proposed as well (e.g., Patent Documents 4 to 7).